Pulp screen plate



Nov. 27, 1934. G.. w. DAvls 1,982,244

PULP SCREEN PLATE Original Filed Nov. 27, 1929 my. 6 .QP/yf INVENT R Patented Nov. `27, 1934 vUNITED STA PULP SCREEN PLATE George w. Davis, seattle, wash.

Application November 27, 1929, Serial No. 410,048 Renewed April 23,` 19.34

4 Claims.

My invention relates to improvements in pulp screens of the form employed for screening wood pulp and other similar pulp which is used in the manufacture of paper.

These screens are usually formed of a plurality of flat screen plates of noncorrosive metal, each provided with a plurality of narrow parallel slots spaced relatively close together. These slots are very narrow, usually ranging from eight thousandths to twelve thousandths of an inch in width and are usually not more than three sixteenths of an inch apart. It is common practice to construct these screen plates from a single or integral piece of flat metal having the narrow slots formed therein by milling said slotsy from thebottom side of the plate. This leaves the end walls ofthe slots curved to conform to the shapeof the milling cutter or circular saw with which theyare cut, and results in the slots `gobeing -shorter on the top side of the bar than fthey would be if .these slot lends could be cut straight through the plate; A serious objection to this method of forming the slots is that, by 'this method, the eiective screening .area of a 'screen plate may be reduced asV much as twenty percent below the maximum area possible of attainment. Another objection to milling the plates in this manner is that the curved and undercut ends of the milled slots form traps in which pulp rand solid l matter may collect and thus further reduce the effective screening area f of the plates. Another objection to this method of constructing the screen plates by milling from a solid metal plate is that it makes diicult the overhaul and repair or reconstruction of the plates in case they become worn or badly clogged or broken, `it being common practice to overhaul plates of this type by re-rolling and re-milling them thus often making necessary a complete .mand expensive overhaul job to correct a slightly worn or broken plate. l

In accordancewith my present invention I correct and overcome theobjectionable features hereinbefore pointed out by making a pulp screen allel relation by tie rods to therebyform a screen plate which is easily disassembled for purpose of cleaning orrepair or replacement of parts, said bars being spaced apart by separate spacers which are short and which obstruct the slots for the least possible distance and which provide vstraight end walls for the slots thus avoiding the formation of traps wherein solid matter may collect. l

plate out of a plurality of vbars which are re-A movably secured togetherin side by side pare Another object of my inventionV is to provide" a pulp screen plate which is plane on both` the top and bottomv and which has no frame members or othermembers projecting above or below thetop and bottom planes of the bars and which is strong enough so that it is self supporting for the purpose of handling, said screen plate being Yarranged to be placed in apulp screen frame when in use and having inclined ends arranged to fit said frame. l

A further object lof my invention is to provide a pulp screen plate in whichthe bars are of substantially T shape in cross section whereby pulsations of water and pulp upward against the bottoms kof said bars `from below will not tend to wedge the pulp in tcthe slots as it might tend to 'do in the case `of wedge shapedbars. l

`These pulp screens are not of large size but are usuallyabout three and one half feetlong and not over twelve inches wide. The bars from which the screens are made are about three eighths of an inch in depth and three sixteenths of an inch wide. These approximate dimensions are given to distinguish this screen from large heavy grate bars and like structures.

Other and more specific objects will be apparent from the following descriptiontaken in `connection with the accompanying drawing.

.In the drawing Figure-1 is a plan view of la `fragment yof va pulp screen plate constructed in 'accordance with my invention.

Fig. 2 isa sectional View of the same substantially on broken line 2-2 of Fig.v 1.

Fig. 3 is a cross section on an enlarged scale onbrokenline `3-'3 of Fig. 1. I

Fig. 4 yis a detached perspective View of one of 90 the gratebars. 1 i

vFig. 5 is ia detached perspective view of one of thespacer plates.

Fig. 6 is aplan view on a small scale of lan entire screen plate" constructed in accor-dance withmy invention.

Fig. 'l is a fragmentary plan 'view on :a smaller scale of a pulp'screen in which the screen bars` extend lengthwise instead of crosswise v`of the Fig. 8 is a fragmentary perspective view showing lan alternative means for securing the screen bars together by the use oftie Ibars' fitted into notches in the ends of the screen bars.

Fig. 9 is la fragmentary perspective view of a 105 `screen bar which' is of T shaped cross section throughout its entire length. u

l Fig. 104 is a sectional view on a larger 'scale vshowing the spacing blocks used in connection with the screen bars shown in Fig. `8,

Referring to the drawing, throughout which like reference numerals designate like parts, Figs. 1 Ito 6 inclusive show a pulp screen plate made up of la plurality of bars detachably secured together so that they may be taken apart for overhauling, cleaning, repairing, or rebuilding. The screen bars are all of duplicate construction, and are shaped like 'a T bar in cross section each having a plane flat top flange or plate 10 Iand a downwardly extending flange or rib 11. At both ends and at a location substantially mid way between the two ends, the screen loa-rs lare provided with Ithickened portions 12 which are flush with Ithe sides of the top web 10 and are provided with perforations 13 through which tie rods 14 may be passed to secure said bars together to form a screen plate. These scr-een b'ars are preferably formed by side milling land leaving the thickened portions 12 the yfull width of the bar. When the bars are assembled thin spacer plates l15 lare inserted `between'thev thickened portions 12 of the ibars to maintain the bars in spaced apart relaftion and to form relatively narrow slots 15 through which the pulpmay pass as it flows over the screen plates. The spacer plates 15 may .be perforated or notched .to 4nt over the tie rods 14. Nuts 17 may provided `on'the tie r-ods 14 at one end for clamping all of the screen bars together. When the screen plates are thus as'- sembled their top surfaces are all flush Iand in lthe' same plane and their bottom surfaces are .all flush and in the same plane and they are s elff supporting and do not need to be reinforced by any frame members in order .to make themstrong enough for the purpose -of .handling and shipment.

lWhen in use the screen plates fare placed in a frame 18, 'as shown by broken linesin .F-ig. V2, and may be bolted down Anr held ingplace :by wedge bars 19 which engage inclined ends 20 ,of the screen bars. Additional 'supportingmembers 19' may Abe provided `under thegscreen bars. For cylindrical screens the screen bars are bent into circles or segments :of circles.

The spacer plates ihave .straightedges which form substantially vertical Iyend walls `21 for the slots `1'6. ,These vertical =en1d walls -tend -tpreyvenlt the formation of :hard masses lof pulp and solid matterin .the lends of the-slots and thush'elp to prevent clogging lup :and reduction :of eiliciency of the screen spiate. If fthe :ends of .these -slots are inclined or ycurved a substantial amount fa trap is formed `|at theends -of the slots nin which below the screen, it zbeing apparent that pulp driven up against the screen Aplate .from below will have less tendency top pass -in-to fthe 'slots where 'a ='l' :barlshapezisused thaniit wouldiif-the space below .the slots converged toward saidslots fand formedra wedge chamber ;forthe pulp to--be driven upwardly into. Due to the lagitationand L'rods -23 are provided-at Afrequent .-intervals. The construction of-.this pulpfscreen plateis otherwise similar to ithe :construction .of .the .screen plate hereinbefore described.

In Fig. 8 I show a perspective view of a frag'- ment of a pulp screen plate in which the screen bars 24 are notched in the ends, as at 25, and a retaining bar 26 is placed in said notches and secured to the bars, as by brazing, to thus serve as a means of holding said bars in assembled relation.

In Figs. 9 and 10 I have shown a fragment of a pulp screen plate in which the bars 28 are T shape throughout their entire length and the spacers are in the nature of blocks 29 arranged to iit between the vertical flanges of the bars and having relatively thin fins 30 thereon aranged to fit between the edges of the horizontal flanges of the bars. `'Ihe advantage of this form of construction lies in the fact that these bars 28 may be made by a process of rolling rather than by milling, thus cheapening the cost of construction and making it possible to form the bars out of more durable material. y

It will be noted that the bars in tjhe screen plates herein disclosed extend overl the enti-re width or entire length of the pla-te ythus avoiding joints or connecting means for the lbars within the area of the pla-tes and contributing to the formation of a stronger and more rigid' and durable screen plate, A

The screen plates may -be quickly and easily taken apart for the purposefof :cleaning or repair and worn or defective bars maybe read-ily replaced with new ones. 'jI'he use of the separate spacers simplifies the construction of the screen bars and makes itpossible -to provide vertical end walls for the slots and'ma-kes it possible to secure a maximum length of o pen slot in proportion -to the length of the bar thus increasing theeleetive screening area on a screen plate of given size.

The foregoing description *and accompanying drawing clearly disclose apreferred embodiment of my invention, Ibut 'itwi'll =b e understood that this disclosure vis merely illustrative and that changes maybe made withinthe scope and spirit of the following claims. f

Iclaim: H f 1. In 'a multiple bar pulp screen plate, va Aplu` rality of `bars of 'l' shaped cross Isection throughout .their entire length, lhaving straight edges lat vboth sides of their Atop flanges arranged yto 4cooperate to form-narrow slots, spacer arranged to Abe interposed at intervals lbetween said bars to maintain said bars -in spaced apart relation, said spacers having wider parts ntting between the bottom Vwebs of said lbarsand narrower parts f1t- Y ting nbetween `thertop flanges `of said bars, 'and tie `rodsf'for `releasably securing la pluralityof said bars together #to form a -screen plate.

2. A pulp screen plate 'embodying -a plurality of relatively narrow "bars Idisposed vside by rside in lparallel relation, said bars having ywider *top 4iianges and lnarrower lower web portions said narrower lower web portions Abeing provided with thickened portions positioned lat the -respective ends and at a location spaced-between said ends, said thickened portions being flush with the sides of Vsaid "wider `top flanges and having transverse 'holes therein,.separable spacer plates .of predetermined thickness `,p0stione.d between said thickened` portions and Asupporting said bars .in `spaced apart .relation Vwhereby k narrow slots 4are provided therebetween, Asaid spacer Aplates each .having .two .edges -formed :at SllbSffiflrl.$125115' ,right ang1es to eachother, one .Qf .Saidedses'being .positioned iilus'h I.with the' top flanges qf the adjacent' barsgandthe`e;dge;at;rieht; anslestheref to Vforming an end wallforthe slot between the adjacent bars, which end wall is perpendicular to the top anges of the bars, said spacer plates each having openings in registration with the holes in said thickened portions and said spacer plates each being relatively short in length whereby a maximum length of slots is aorded, and tie rods extending through the thickened portions of the bars and through the spacers whereby all of the bars are secured together at their ends and at a location between their ends.

3. A pulp screen plate of the class described, embodying a plurality of relatively narrow bars disposed side by side in parallel relation, said bars having Wider top flanges and narrower lower web portions, said narrower lower web portions being provided with thickened portions positioned at the respective ends of said bars and at a location spaced between said ends, said thickened portions being flush with the sides of said wider top flanges and having transverse holes therein, separable spacer plates of predetermined thickness positioned between said thickened portions and supporting said bars in spaced apart relation whereby narrow slots are provided between said bars, said spacer plates each having two edges formed at substantially right angles to each other one of said edges being positioned flush with the top flange of the adjacent bars and the edge at right angles thereto forming an end Wall for the slot between the adjacent bars, which end wall is perpendicular to the top flanges of the bars, said spacer plates each having openings in registration with the holes in said thickened portions and said spacer plates each being relatively short in length whereby a maximum length of slot is afforded, and tie rods extending through the thickened portions of said bars at the respective ends of the bars and at the location which is spaced between the ends of the bars whereby said bars are all secured together and a pulp screen plate which is self supporting without additional frame means is formed, said bars all being of equal depth with their top and bottom edges terminating in a common plane whereby a pulp screen plate having two plane surfaces free from protruding members is afforded.

4. A multiple bar pulp screen plate, embodying a plurality of relatively narrow bars of T shape cross section disposed side by side in parallel relation, separable spacer members of predetermined thickness positioned between said bars and supporting said bars in spaced apart relation whereby narrowslots are provided between said bars, said spacer members each having two straight edges formed at substantially right angles to each other, one of said edges being flush with the top flanges of the adjacent bars and the edge at right angles to said flush edge being positioned between the adjacent bars and forming an end wall for the slot between the bars, which end Wall is at right angles to the length of the bars, and tie rods extending'through said bars and said spacer members whereby said bars are detachably secured together' to form a self supporting pulp screen plate capable of being dis-assembled for reconstruction. y l

GEORGE W. DAVIS. 

